I think the PM function needs to be adaptive. Currently you can be part of a team or PM privately. I am currently playing a game where we have groups (EU/North American Alliance/Etc)but these groups are fluid (Russia and the Balkans have asked to leave the EU)

In our game we are being threatened by the Balkans. As the largest land owner in the EU I currently control it but everything is put to a vote. I have had to message every member individually to ask for a vote on declaring war. It would be amazing if we had a group for each faction, and if people join/leave the faction then they get access to the chat. If they leave they no longer get messages, if they join then they don't get access to previous messages.

Just an idea on how our diplo game could be massively improved, it would also work in other games, if you form an alliance then a group is automatically created. If you are invited to join the alliance then the leader (plus yourself) must accept the invite.